Feature of theatre role — having boob exposed at the start (8)
I believe the answer is:
parterre
'feature of theatre' is the definition.
(parterre can mean a part of a theatre)
'role having boob exposed at the start' is the wordplay.
'role' becomes 'part' (eg a part or role in a film).
'having' means one lot of letters go next to another.
'boob' becomes 'err' (both can mean to make an error).
'at the start' suggests taking the first letters.
The first letter of 'exposed' is 'e'.
'part'+'err'+'e'='PARTERRE'
(Other definitions for parterre that I've seen before include "Part of the main floor of a theatre" , "level ground" , "Formal garden feature" , "The pit or bottom floor of a theatre" , "Flower bed or beds" .)